1. Field of the Invention
The invention relates to a method and apparatus for positioning a pile driving head from a vessel onto the top of a pile or similar body at a considerable depth under water. The pile driving head is lowered on guide cables which run downwards from the vessel towards the pile and are secured in such a manner that the pile driving head is positioned over the pile.
2. Description of the Prior Art
The prior art discloses the method of lowering a pile driving head onto the top of a previously positioned pile which has its lower end inserted into the bore of a caisson placed on the ocean bottom to hold the pile in the correct position for pile driving. The pile driving head is lowered towards the pile being guided by cables running from the vessel towards the caisson which are kept taut by means of swell compensators. If the vessel remains directly over the pile, the pile driving head can be lowered over the pile without difficulty. In practice, deviations in a lateral direction will occur, with the result that the guide cables at the level of the top of the pile are laterally displaced from the pile. Consequently, the pile driving head canot be lowered directly over the pile.
This problem does not occur only when moving a pile driving head towards a pile but wherever guide cables are used to position a device onto a section of a previously lowered body. Pile driving at great depths causes considerable problems necessitating the assistance of divers, underwater television and sonar to determine the position of the cables with respect to the pile. If the piles are of considerable length, e.g., 100m, there may be a substantial deviation between the guide cables and the top of the pile.